1. Field of the Invention
Solid detergents for dishwashing machines are sold predominantly in powder or granulate form (agglomerates). The individual particles of these detergents have a preferred diameter of from 0.01 to 3 mm. A serious disadvantage of solid detergents of this type, particularly those used institutionally with an alkali hydroxide content of from 10 to 60% by weight, is that, on account of the hygroscopicity of individual raw materials, they show a pronounced tendency towards caking or clumping in the presence of small quantities of moisture.
By adding so-called "anticaking" agents, such as paraffin for example, or by coating highly hydroscopic constituents, such as for example the alkali hydroxides and the sodium metasilicate, with powdered substances, such as for example pentasodium triphosphate or sodium sulfate, it is possible to obtain slight improvements (i.e. reduction) in the caking or clumping behavior, although relatively large quantities of moisture in the form of water or water vapor still lead to caking or clumping of the powdered or granulated detergents.
Although this does not make the detergents unusable, because the effect of the individual constituents remains intact even after clumping or caking in the presence of moisture, the appearance of the detergents in most cases is diminished or inferior in the eyes of the consumer, resulting in complaints.
The use of detergents which cake or clump in the presence of moisture is a particular disadvantage in automatic, dispenser-type metering units which are used in large numbers in institutional single-tank and multi-tank dishwashing machines. Metering problems arise either because too little detergent is dispensed or because the dispenser system itself is mechanically damaged and becomes unusable. The only remedy is to prevent moisture from entering the storage compartment, although this cannot be guaranteed in the moist atmosphere of kitchens or after the machine has been cleaned with water without special drying of the storage compartment and the dispenser.
The clumping or caking of alkaline detergents can be avoided inter alia by preparing them in block form from the outset and packaging, marketing and using them in highly moisture-proof form.
However, this does not in any way solve every problem because compounds containing active chlorine are extremely difficult to incorporating in strongly alkaline detergents.
2. Description of the Prior Art
European Patent Specification No. 3,769 describes detergent containers, more especially for dishwashing machines, which contain solid detergent blocks produced from water and two solid constituents, of which at least one is an alkaline hydratable compound, and which are only open at one point from which the detergent is subsequently flushed out into the dishwashing machine by the stream of water. If, in addition to alkali hydroxides, these detergents are intended to contain active chlorine compounds which are regarded as necessary for the removal of bleachable soil, such as for example tea, coffee, fruit juices etc., they have to be introduced, preferably as preformed cores, into the soft mass during solidification of the detergent. In order more effectively to protect the chlorine donor, the core is said to be coated either with paraffin or with a wax-like mono- or dialkylester of polyphosphoric acid. The direct incorporation of compounds containing active chlorine, particularly in the presence of high concentrations of alkali hydroxide, is regarded as impracticable. In Example 13, Table 1, it is shown that the direct addition of an active chlorine donor to the melt leads to a high loss of active chlorine in only 24 hours. The chlorine donors tested were Ca(OCl).sub.2, LiOCl and Na-dichloroisocyanurate dihydrate. Residual chlorine activities of from only 3.5 to 17.4% of the original value were determined, depending on the chlorine donor.
Although the incorporation of preformed cores containing active chlorine donors is possible, it involves high costs through labor-intensive production and the necessary raw materials. In addition, the detergent blocks and their cores naturally differ in solubility.
U.S. Pat. No. 2,412,819 describes briquetted detergents containing alkali hydroxide for dishwashing machines which are produced by mixing together with all the other alkaline-reacting active substances, such as for example sodium silicates and pentasodium triphosphate, and, optionally, water, if the preferred water of hydration in the compounds mentioned is not sufficient, and then gently heating the mixture with stirring to 90.degree. to 100.degree. C. until a uniformly molten mass is formed, pouring this melt into molds and allowing it to solidify into a compact crystal aggregate therein. There is no mention of active chlorine donors in these briquetted detergents.
Another disclosure of interest is U.S. Pat. No. 3,816,320 which indicates that sodium dichloroisocyanurate dihydrate is superior to the anhydrous salt, but again, this disclosure is not concerned with the fused block detergents of this invention which employs alkali hydroxides.
U.S. Pat. No. 3,390,092 discloses dishwashing detergents in tablet from which contain sodium or potassium dichloroisocyanurate. The composition minimizes decomposition by using paraffin oil and sodium silicate or a very fine material having an average particle size of 74 microns or less. The compositions of this patent are also devoid of the strong alkali-hydroxides required for the fused block compositions of this invention.